The present invention relates in general to leather skin covered interior trim components for vehicles, and, more specifically, to pre-weakening of a tear seam in a leather cover skin without mechanical cutting or removal of leather material at the seam.
Passenger vehicles often provide airbag assemblies that deploy through interior trim panels such as an instrument panel, door panel, door pillars, seats, and roof liners. During an impact condition, the airbag is deployed for cushioning an occupant thereby enhancing safety. One typical instrument panel includes a rectangular opening having one or more hinged doors within the opening. The hinged doors are arranged to pivot from the instrument panel as an airbag deploys, forcing the doors outward. Such an instrument panel may include a rigid substrate, a layer of foam, and a layer of skin. The foam layer is typically injected between the substrate and the skin layer. Upon opening of the door(s), it is necessary that the skin and foam layers tear away in order to permit opening of the door(s) and passage of the air bag emerging from behind the panel. To assist in tearing, a pre-weakened tear seam is typically provided in the skin and foam layers.
For styling purposes, it is desirable for the air bag deployment door and the pre-weakened tear seam to be invisible when viewed from the passenger compartment. In other words, the visible or “Class A” surface of the instrument panel is preferably seamless. Therefore, the pre-weakened tear seam is formed on a hidden surface of the skin (on the “Class B” side), preferably in a manner that leaves the unhidden Class A surface undistorted.
The most commonly used materials for making panel cover skins for passenger vehicles have been various polymers including urethane. The skins have been molded or cast and then mechanically scored along a tear seam. Mechanical scoring includes cutting (i.e., scribing) into a surface with a knife blade (which can be cold or heated or vibrated ultrasonically) or with a laser. It is also know to remove material by chemical means. In some instances, scoring is conducted simultaneously for the substrate, foam layer, and skin layer by scanning with a laser.
In luxury vehicles, it is more common to utilize a natural leather to provide the skin layer. Leather skin can be provided with a foam layer or can be hard wrapped without a foam layer. Due to the properties of leather (such as variability in the skin thickness), creation of a tear seam which remains invisible on the Class A surface is more difficult. In particular, removal of material or direct mechanical cutting into the surface has a risk of “read-thru” at the visible side. Examples of mechanical alteration of the leather skin from the hidden surface include U.S. Pat. No. 8,132,307 and U.S. Pat. No. 7,497,463. It would be desirable to improve tear seam performance and to provide associated manufacturing techniques that maintain low cost and reliable results.